In recent years, sputtering is extensively used for formation of thin films, and composite targets composed of at least two components are demanded to provide in thin films with high performance and/or high value added.
Sputtering targets have been produced so far by melting, hot pressing and atmospheric pressure sintering. However, when these conventional techniques are employed for production of composite targets composed of a high-melting substance such as a high-melting metal or ceramic, and a low-melting substance, uniform and dense targets do not result because of the phase separation due to different densities of the components, the compositional change due to the different melting points of the components, exudation of the molter low-melting metal and other problems.
Although a process in which a mixture of a powder of a high-melting substance with a powder of a low-melting metal is molded at room temperature under pressure (Japanese unexamined patent application JP-A-4-323366) is known, the process requires high pressures of 1000-3500 kgf/cm.sup.2 or above for production of dense targets and is unsuitable for production of large targets and mass production.
Further, since the modeling operation at room temperature under pressure induces residual stress in a target produced by the process, sputtering targets produced by the process have a problem of their poor in dimensional stability which emerges as a permanent elongation of 0.5-2% based to on the length of the targets due to thermal hysteresis during bonding or film formation, and a problem of racking and peeling during sputtering.
On the other hand, production. of dense targets from a mixture of a powder of a high-melting substance with a powder of a low-melting metal by uniaxial pressing at room temperature, which is usually employed in molding ceramics, requires a very large machine which would cost too much to avoid a tremendous increase in the production cost, and is, therefore, impractical.
Therefore, the object of present invention is to provide composite dense targets composed of a high-melting substance and a low-melting metal without using a large machine by an economical process which solves the above-mentioned drawbacks of the prior art.